1. Field of the Invention
The invention relates to the ear piece of a hearing aid, namely the portion which is inserted into the external ear canal. The ear piece may be the hearing aid itself, for example, a canal hearing aid or an in-the-ear hearing aid; or an attachment, such as the end of a flexible sound tube of a behind-the-ear hearing aid. The ear piece often is molded to fit an individual's ear canal and sometimes has a compressible, resilient sleeve for enhanced comfort. Such a sleeve is often employed to permit one or a few ear pieces to fit nearly everyone, as do ear pieces of the invention.
2. Description of the Related Art
The problem of providing a hearing aid with an ear piece that can be continuously worn with comfort has long been a subject of research. See, for example, U.S. Pat. No. 1,743,817 (Aber). There, an impression of an individual's ear canal was used to mold an ear piece (there called an "audiphone cap"). Such a procedure is still in widespread use, even though time-consuming and expensive and requiring two visits to fit a person with a hearing aid. Moreover, the resulting ear piece is rigid, uncomfortable to wear, and prone to falling out of the ear canal.
U.K. Patent Application No. 2,091,063 (Blackstone) discloses the use of a layer of cushioning material, preferably one providing a high coefficient of friction, to seal a small gap between the external surface of a molded ear piece (called a "plastics molded component") and the internal surface of the ear canal, and PG,3 to eliminate any whistling sound or echo effect. The molded ear piece approximates the shape of the external ear canal. Only a thin layer of the cushioning material is employed with the result that it does not provide a truly comfortable fit.
FIGS. 14-18 of U.S. Pat. No. 4,375,016 (Harada) show a layer of cushioning material in the form of a sleeve which fits over the distal end of the ear piece and is said to provide excellent fit without the necessity of using a custom molded construction. That sleeve is "formed from a compressible foam with characteristics as shown in U.S. Pat. No. Re. 29,487." The foam "can be compressed to a diameter less than that of the auditory canal. As the foam slowly attempts to return to its original configuration, it seals the auditory canal in a comfortable fashion as shown in FIGS. 17 and 18" (Col. 4, lines 41-56). However, the Harada patent does not indicate how the sleeve is prevented from remaining in the ear canal if the ear piece is either accidentally dislodged from the ear canal or simply pulled out. Rather than dealing with such matters, the Harada patent concentrates on the venting of excess sound pressure from the ear canal to the atmosphere.
The reissue patent (Gardner, Jr.) cited in the Harada patent does not concern hearing aids but describes an "earplug . . . composed of a resilient, plasticized polymeric foam containing a sufficiently high concentration of organic plasticizer to provide the foam with a rate of recovery from 60 percent compression to 40 percent compression in from 1 to 60 seconds and an equilibrium pressure at 40 percent compression thereof from 0.2 to 1.3 p.s.i." (claim 1). Cylindrical plugs of this material can be coaxially bored and employed as a covering over a tubular tip portion of a lightweight headphone set. However, like the Harada patent, Gardner does not indicate how the plug is prevented from remaining in the ear canal if the tubular tip portion is accidentally dislodged or simply pulled out.
Despite the approaches discussed above, none have been truly effective, particularly from the standpoint of providing an ear piece which is comfortable, retained during use, and readily removable when desired. Moreover, none have addressed a continuing problem in the hearing aid art, namely clogging of the sound tube by ear wax. Approximately half of professional repairs of hearing aids are either to remove ear wax or to repair damage caused by a user who tried to clean out the wax. That problem has been addressed in U.K. Patent Application GB 2,155,276A (Brander et al.); West German Offenlegungsschrift 2,818,273 (Sommer); and EPO Patent Application 85103722.6 (Laid open No. 0,159,571) (Moser et al.).